Multi material secondary metallization scheme in MEMS fabrication

Abstract

Processes are provided herein for the fabrication of MEMS utilizing both a primary metal that is integrated into the final MEMS structure and two or more sacrificial secondary metals that provide structural support for the primary metal component during machining. A first secondary metal is thinly plated around the primary metal and over the entire surface of the substrate without using photolithography. A second secondary metal, is then thickly plated over the deposited first secondary metal without using photolithography. Additionally, techniques are disclosed to increase the deposition rate of the first secondary metal between primary metal features in order to prevent voiding and thus enhance structural support of the primary metal during machining.

1. A process for fabricating a multi-layer micro-electro-mechanical system, comprising:
 a) providing a primary metal structure supported by a substrate; 
 b) depositing a first sacrificial secondary metal in a thin layer around the primary metal structure and over the entire surface of the substrate; 
 c) depositing a second sacrificial secondary metal in a thick layer around first sacrificial secondary metal and over the entire surface of the substrate; 
 d) machining the primary and first and second sacrificial secondary metals; 
 e) repeating steps (a)-(d) above until a desired multi-layered structure is fabricated; and 
 f) etching away the first and second sacrificial secondary metals from the machined primary metal structure to form a multi-layered micro-electro-mechanical system; 
 wherein the deposited second sacrificial secondary metal is of a lower density than the first sacrificial secondary metal, such that the combination of these metals does not cause the substrate to warp. 
 
     
     
       2. The process of  claim 1 , wherein the etching away of the first and second sacrificial secondary metals does not substantially etch the machined primary metal structure. 
     
     
       3. The process of  claim 2 , wherein both the first and second sacrificial secondary metals are etched away using the same etching agent. 
     
     
       4. The process of  claim 1 , wherein the deposited first and second sacrificial secondary metals provide horizontal mechanical support to the primary metal during machining. 
     
     
       5. The process of  claim 1 , wherein the primary metal comprises nickel. 
     
     
       6. The process of  claim 1 , wherein the first and second secondary metals comprise copper. 
     
     
       7. The process of  claim 1 , wherein the primary metal structure comprises cavities along its surface area and the rate of deposition of the first sacrificial secondary metal is faster within the primary metal structure's cavities than outside of the cavities. 
     
     
       8. The process of  claim 7 , wherein the deposited secondary metal lacks significant voiding. 
     
     
       9. The process of  claim 7 , wherein the deposited sacrificial secondary metal is electroplated from a plating bath comprising organic additives selected from the group consisting of brighteners, levelers, and suppressants. 
     
     
       10. The process of  claim 9 , wherein the plating bath comprises copper at 50 g/L, acid at 80 g/L, chloride at 50 ppm, a brightener at 12 mL/L, a suppresser at 2 mL/L, and a leveler at 3 mL/L. 
     
     
       11. The process of  claim 1 , wherein the micro-electro-mechanical system is a spring that can be used in conjunction with a probe card assembly to test semiconductor devices.